The present invention relates to an apparatus for robustly controlling a plant against disturbance.
The amount of air introduced into an engine is typically controlled so as to achieve a desired engine torque. According to a conventional method, a desired amount of air introduced into the engine is determined referring to a map based on an opening angle of an accelerator pedal, a vehicle speed and a selected transmission gear ratio. An opening angle of a throttle valve is controlled in accordance with the desired amount of air to be introduced into the engine.
According to another method disclosed in Japanese Patent No. 2780345, a desired torque of an engine output shaft is determined in accordance with an opening angle of an accelerator pedal and a rotational speed of the output shaft of a torque converter. A desired opening angle of a throttle valve is determined referring to a predetermined table based on an actual rotational speed and the desired torque of the engine output shaft. Air is introduced into the engine in accordance with the desired throttle opening angle.
Such conventional control does not take into account disturbance applied into the intake manifold and dead time from the throttle valve to the engine. Such factors reduce the accuracy of controlling air to be introduced into the engine, causing vibration in the engine torque.
Such a problem regarding robustness against disturbance exists in rotational speed control for the engine.
Conventionally, when an engine is idling, a conventional PID control is performed for controlling an engine rotational speed. According to such conventional rotational speed control, when a sudden change in the engine load occurs during idling operation, the engine tends to stop because the engine rotational speed cannot be stable. For example, when a vehicle with a manual transmission mechanism starts and a clutch is forced to engage suddenly, the engine of the vehicle tends to stop.
Japanese Patent No. 3203602 discloses a scheme for reducing shock that may make passengers of the vehicle uncomfortable when gear change occurs in an automatic transmission mechanism. According to the scheme, a desired torque of a driving shaft is determined based on a vehicle speed and an opening angle of the accelerator pedal. A desired engine torque and a desired engine rotational speed that provide the desired driving shaft torque are determined. An opening angle of the throttle valve is determined based on the desired engine torque and the desired engine rotational speed. The throttle valve is controlled in accordance with the determined opening angle.
Conventionally, in a vehicle that comprises an automatic manual transmission (automatic MT) or an automatic transmission (AT), when gear change occurs, a rotational speed synchronization control capable of achieving a quick response is not performed. Thus, a rotational speed cannot be adapted to a selected transmission gear ratio quickly.
Thus, there is a need for control that has high robustness against disturbance.